Process for improving stress corrosion cracking resistance of alloyed steel in hydrogen sulphide atmosphere



y 1959 P. G. BASTIEN PROCESS FOR IMPROVING STRESS CORROSION CRACKINGRESISTANCE OF ALLOYED STEEL IN HYDROGEN SULPHIDE ATMOSPHERE Filed Nov.13, 1957 lOO T IME 1N HOURS I F1G TESTS OESTRESS-CORROSLON CRACKING WITHHYDROGEN SULFLDE Fl G .ZBRELATIVE REDUCTION IN AREA BY HYDROGENATION 2Sheets-Sheet 1 H v N 8 YLELD POINT E Kg *mm 5o 6O 1o YLELD PO INT E KgTnm I INVENTUR 1 M 9% 13mm,

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ATTORNEYS I July 21, 1959 P. G. BASTIEN PROCESS FOR IMPROVING STRESSCORROSION CRACKING RESISTANCE OF ALLOYED STEEL IN HYDROGEN v SULPHIDEATMOSPHERE Filed Nov. 13, 1957 2 Sheets-Sheet 2 AREA OF UTILITY OF STEELLN THE PRESENCE OF HYDROGEN SULF'IDE F G 5 AMOUNT OF CARBON RECOMMENDEDNOT SATISFACTORY H A r- Q 2 E z m 6i 6% KL cn Q4 m x: Q I Q ,4 2 A M a 8W m i M x TEST SAMPLE CRACKED ACCEPTABLE LIMIT SHOWN AMOUNT OF CARBONRECOMNLENDED BY HYDROGENATION TESTS k 80 NOT SATISFACTOR t 75 a Q 52 E si E To 5? 2 a 8 m u 06 m4 :2 :2 m INVENTOR V AMOUNT or CARBON F 1c; 4 Mmzam BY W,W

ATTORNEYS United States Patent PROCESS FOR IMPROVING STRESS CORROSIONCRACKING RESISTANCE F ALLOYED STEEL 1N HYDROGEN SULPHIDE ATMOSPHERE PaulGaston Bastien, Paris, France, assign'or to Socit des Forges et Ateliersdu Creusot, Paris, France, a company of France Application November 13,1957, Serial No. 696,261

Claims priority, application France May 28, '1957 7 Claims. (Cl.148-215) This invention relates to the manufacture of elements fromalloyed steel, and is more particularly concerned with the manufactureof parts possessing superior tensile properties and required towithstand cracking due to stress corrosion in a moist atmosphere ofhydrogen sulfide, in the presence or absence of carbonic gas, andgenerally in a medium conducive to embritfllement of the steel byhydrogen.

In the course of well drilling operations for the recovery of petroleumor natural gas, for example, the tubes used for this purpose often comein contact with a moist and hot medium charged with hydrogen sulfideunder pressure. Also the parts of steel employed in installations fortreating petroleum products or natural gas, may come into contact with aliquid or gaseous medium that causes embrittlement of the seel, as forexample a medium more or less saturated with hydrogen sulfide underpressure and at temperatures often in excess of the ambient temperature.

These conditions are very detrimental to the steel in that they giverise, after a more or less extended period, to the formation of cracksresulting from the superposition of mechanical stresses and theembrittlement induced by the hydrogen arising from the corrosion byhydrogen sulfide.

It has been found that the cracks in most cases resulted from astructure of insufficiently stable metal, comprising particularlyincompletely tempered martensite or residual austenite dispersedthroughout the mass.

Moreover, especially for application in well bores. of great depth forthe recovery of petroleum or natural gas, it is indispensable to obtainsteel possessing superior tensile properties.

In order to avoid cracking, attempts have been made to use steels thatheretofore presented difiiculties in manufacture and particularly in thetreatment thereof. On the other hand, the problem of obtaining superiortensile properties has remained, for the time being, difficult to solve,especially when it comes to producing a steel that will continuouslywithstand the formation of cracks.

The present invention makes it possible to obtain a steel havingsatisfactory tensile properties which is capable of resisting crackingin the presence of hydrogen sulfide even under pressure and attemperatures in excess of the ambient temperature.

It has been found that it is possible to employ a steel of thechromium-molybdenum-vanadium type confined heretofore to uses in otherfields, on condition that it is subjected to a treatment especiallychosen in contemplation of the particular conditions encountered duringthe use thereof referred to above.

According to the invention, the process comprises the utilization of asteel having the following composition by weight:

Percent C 0.10 to 0.25 Si 0.10 to 0.50 Mn 0.30 to 1.0

Percent Cr '1 to 14 Mo 0.4 to 1.5 V 0.10 to 0.60 Ni 0 to 1 the remainderbeing substantially all iron except for minor quantities of otherelements such as sulfur up to 0.030%, phosphorus up to 0.025%, copper upto 0.20%, and a two-stage thermal treatment of this steel. The firststage of the heat treatment consists in an austenitization at atemperature from 975 to 1100" C. for a period of about one hour or less(from 1 to 5 minutes in the case of tubes), followed by a cooling step(hardening) conducted at an average speed at least equal to 30 C. perminute between 850 and 600 C., and the second stage consists intempering at a temperature from 725 to 800 C. for a period producing ayield point between 55 and 65 kg./mm.

It has been found that the yield point E should not be greater than 65kg./mm. for steel which is resistant to stress corrosion cracking in thepresence of hydrogen sulfide as shown by the curve of Figure 1. Fromthis figure it is seen that the time required for cracking increases asthe yield point decreases. I

The relative reduction in area (percent) by hydrogenation increases asthe yield point decreases or increases from optimum values between 58and 65 kg./mm. as is seen in Fig. 2.

When the steel is employed in tubes the two heat treatments describedabove are applied after the tubes are formed.

According to the invention, it is thus contemplated to use a hardenablesteel which can endure a tempering treatment at high temperature whilestill preserving its superior tensile properties, and having impartedthereto a thermodynamically stable structure necessary for stresscorrosion cracking resistance.

The tensile properties of this stable structure, such as the value of Rwhich is the ultimate strength applied, and the yield point define thearea of utility of these chrome-molybdenum-vanadium steels as a functionof the amount of carbon as shown in Figs. 3 and 4.

The invention will now be described in greater detail with reference tospecific examples.

Example I Test pieces were made from a steel having the followingcomposition by weight:

This steel is intended for contact with a saturated solution of hydrogensulfide.

It was subjected to the following treatment:

First treatment stage: Austenitization at a tempera- .ture'of from 980to 1000 C. for about one hour, followed by air cooling (hardening) at anaverage speed at least equal to 30 C. per minute between 850 and 600 C.

Second treatment stage: Tempering at a temperature 7 of approximately750 C. for about one hour.

The tensile properties thus obtained are as follows:

Yield point E=62 kg./mm. Ultimate strength R=72 kg./mm.

Elongation A=24% (the useful length of the test piece being equal tofour times its diameter).

The'structure of the steel treated in the above manner is compo'sed'offine spheroidized carbide particles uniformly distributed in theferritic matrix. Such a structure becomes readily apparent when it issubjected to the action of an alcohol solution of picric acid.

The steel treated in this manner was tested in contact witha saturatedsolution of hydrogen sulfide containing 0.5% by volume of acetic acid,the latter functioning to accelerate and aggravate the corrosion. Themetal was submitted to a permanent flexur'e when using a two point beamloaded specimen, the maximum stress being slight- 1y higher than theyield point of the metal under flexure. No cracks were observed after3000 hours of this treatment.

On the other hand, in the case of tempering temperatures below 725 C. ortoo short tempering periods which impart to the metal a yield pointabove 65 kg./mm. fractures were obtained in less than 500 hours.

Example 11 Test pieces were obtained in a steel having the followingcompositions by weight:

This steel was subjected to the following treatment:

First treatment stage: Austenitization at 980 followed by air cooling(one half hour).

Second treatment stage: T empering at a temperature of 725 C. for onehour.

The yield point of the steel was E=71.2 kg./mm.

This steel was placed in contact with a saturated solution of sulfuricacid and maintained under fiexure. A crack developed after 112 hours andtwo cracks developed in 300 hours.

A steel of the same composition was subjected to the followingtreatment:

First treatment stage: Austenitization at 980 followed by air cooling(one half hour).

Secondtreatment stage: T empering at a temperature of 750 C. foronehour.

The yield point of the steel-was E=60 kg./mm.

This steel was placed in contact with a saturated solution of sulfuricacid and was maintained under flexure. No cracking was noted in 2000hours.

Example III Test pieces'we're obtained in a steel having the followingcomposition by weight:

This steel was submitted to the following treatment:

First treatment stage: Austenitization at 980 C followed by air cooling(one hour).

Second treatment stage: T empering at a temperature of 725 C. for onehour.

The yield point of the steel was E=67.1 kg./mm.

The steel was placed in contact with a saturated solution of sulfuricacid and was maintained under fiexure. A crack was observed at 320hours. No other cracks were produced in 3300 hours.

A steel having the same composition was submitted to the followingtreatment:

First treatment stage: Austenitization at 980 followed by air cooling(one half hour).

Second treatment stage: Tempering at a temperature of 725 C. for twohours.

The yield point of this steel was E=63.2 kg./m.m.

This steel was placed in contact with a saturated solution of sulfuricacid and was maintained under flexure. No cracking was observed after4000 hours.

Example IV Tubes were made from a steel having the followingcomposition:

Percent C 0.14 Si 0.14 Mn 0.45 Cr 2.49 M0 0.90 V 0.22 S 0.011 P 0.020 FeRemainder These tubes are intended for use in petroleum wells Yieldpoint E=60 kg./mm. Ultimate strength R=69 kg./mm. Elongation A=25% (testpieces made of the steel of the tubes having a useful length equal tofour times'their diameter).

The structure of the steel is analogous to that indicated in Example 1.

Test pieces, made of the metal of the tubes of the present example andgiven the same treatment, were then subjected to the test described inExample I. No cracks were observed after 3000 hours.

Example V Test pieces were made from a steel having the followingcomposition by weight:

Percent C 0.20 Si 0.23 Mn 0.52 Cr 11.5 Mo 1.10 V 0.30 Ni 0.40 S 0.015 P0020' Fee Remainder This steel is intended for contact with a solutionof hydrogen sulfide. The high chromium content of this steel is for thepurpose of improving its resistance to generalized corrosion, i.e., toreduce the loss in thickness of parts during service.

The steel was subjected to the following treatment:

First treatment stage: Austenitization at a temperature of approximately1000 C. for about 15 minutes, followed by cooling with air at least atthe rate specified in Example I.

Second treatment stage: Tempering at a temperature of approximately 775C. for about one hour.

The tensile properties obtained are as follows:

Yield point E=61 kg./mm. Ultimate strength R=82 kg./mm. Elongation A=25%(the useful length of the test piece being equal to four times itsdiameter).

The structure of the steel is analogous to that indicated in Example I.

The steel thus treated was tested in the manner described in Example I.No cracks were observed after 3000 hours.

It is to be understood that the examples given above are indicative ofonly a few specific applications of the invention. The temperatures andthe duration of the treatments above indicated may vary within certainlimits without departing from the principles underlying the invention.

Insofar as the austenitization temperature is concerned, it should varyonly from 975 to 1100 C. As to the tempering temperature, it should varyonly in the range between 725 and 800 C.

The choice of the preferred temperatures to be used within these ranges,as well as the duration of the tempering step, must depend upon theyield point to be obtained which lies between 55 and 65 kg./mm.according to the amount of carbon (see Fig. 3).

Finally, in the preceding examples it was indicated that the coolingcould be effected either with air (Examples 1, H, III and V) or withwater (Example IV). The choice of the cooling medium obviously dependsupon the shape and thickness of the structural parts since the coolingmust be sufiiciently rapid to insure the hardening of the steel.

What is claimed is:

1. A process for manufacturing an alloyed steel element having finespheroidized carbide particles uniformly distributed in the ferriticmatrix capable of stress corrosion cracking resistance in a moistatmosphere charged with hydrogen sulfide including the steps ofaustenitizing an alloyed steel element having a composition comprisingfrom 0.10 to 0.25% carbon, from 0.10 to 0.50% silicon, from 0.30 to 1.0%manganese, from 1 to 14% chromium, from 0.40 to 1.5% molybdenum, from0.10 to 0.60% vanadium, from to 1% nickel, and minor quantities of otherelements such as sulfur up to 0.030%, phosphorus up to 0.025%, copper upto 0.20%, the remainder being substantially all iron, at a temperaturebetween 975 and 1100 C., cooling the steel at a speed at least equal to30 C. per minute between 850 and 600 C., and then tempering the steel ata temperature between 725 and 800 C. for a period of time sufiicient toproduce a yield point between 55 and 65 kg./mm. according to the amountof carbon.

2. A process as defined in claim 1 wherein the austenitizing treatmentis conducted at a temperature between 980 and 1000 C. for a period ofabout one hour.

3. A process as defined in claim 1 wherein the austenitizing treatmentis conducted at a temperature between 1000 and 1050 C. for a period ofabout 1 to 5 minutes.

4. A process as defined in claim 1 wherein the tempering treatment isconducted at a temperature of approximately and not less than 750 C. fora period of about one hour.

5. A process for manufacturing an alloyed steel element having finespheroidized carbide particles uniformly distributed in the ferriticmatrix capable of stress corrosion cracking resistance in a moistatmosphere charged with hydrogen sulfide including the steps ofaustenitizing an alloyed steel element having a composition comprisingabout 0.17% carbon, 0.30% silicon, 0.50% manganese, 2.5% chromium, 1%molybdenum, 0.25% vanadium, 0.2% nickel, 0.02% sulphur and 0.015%phosphorus, the remainder being substantially all iron, at a temperaturebetween 980 and 1000 C. for a period of about one hour, cooling thesteel at a speed at least equal to 30 C. per minute between 850 and 600C., and then tempering the steel at a temperature of approximately butnot less than 750 C. for a period of about one hour.

6. A process for manufacturing an alloyed steel tube having finespheroidized carbide particles uniformly distributed in the ferriticmatrix capable of stress corrosion cracking resistance in a moistatmosphere charged with hydrogen sulfide including the steps ofaustenitizing an alloyed steel tube having a composition comprisingabout 0.14% carbon, 0.14% silicon, 0.45% manganese, 2.49% chromium,0.90% molybdenum, 0.22% vanadium, 0.011% sulphur and 0.020% phosphorus,the remainder being substantially all iron, at a temperature between1000 and 1050 C. for a period of about 1 to 5 minutes, cooling the steelat a speed at least equal to 30 C. per minute between 850 and 600 C, andthen tempering the steel at a temperature of approximately but not lessthan 750 C. for a period of about one hour.

7. A process for manufacturing an alloyed steel element having finespheroidized carbide particles uniformly distributed on the ferriticmatrix capable of stress corrd sion cracking resistance in a moistatmosphere charged with hydrogen sulfide including the steps ofaustenitizing an alloyed steel element having a composition comprisingabout 0.20% carbon, 0.23% silicon, 0.52% manganese, 11.5% chromium, 1.1%molybdenum, 0.30% vanadium, 0.40% nickel, 0.015% sulphur and 0.020% phosphorus, the remainder being substantially all iron, at a temperature ofapproximately 1000 C. for a period of about 15 minutes, cooling thesteel at a rate at least equal to 30 C. per minute between 850 and 600C., and then tempering the steel at a temperature of approximately butnot less than 775 C. for a period of about one hour.

References Cited in the file of this patent UNITED STATES PATENTS1,700,674 Fry Ian. 29, 1929 1,876,091 Strauss Sept. 6, 1932 2,645,574Clark July 14, 1953 FOREIGN PATENTS 371,633 Great Britain Apr. 28, 1932338,556 Italy Mar. 31, 1936 213,758 Switzerland June 3, 1941 OTHERREFERENCES Lillys et al.: Transactions of the American Society forMetals, vol. 48, preprint No. 30 (received in the Patent OfiiceSeptember 20, 1955). Published by the American Society for Metals,Cleveland, Ohio.

Hildorf et al.: Transactions of the American Society for Metals, vol.27, 1939, pages 1090-1117. Published by the American Society for Metals,Cleveland, Ohio.

1. A PROCESS FOR MANUFACTURING AN ALLOYED STEEL ELEMENT HAVING FINESPHEROIDIZED CARBIDE PARTICLES UNIFORMLY DISTRIBUTED IN THE FERRITIC INA MOIST ATMOSPHERE CHARGED SION CRACKING RESISTANCE IN A MOISTATMOSPHERE CHARGED WITH HYDROGEN SULFIDE INCLUDING THE STEPS OFAUSTENITIZING AN ALLOYED STEEL ELEMENT HAVING A COMPOSITION COMPRISINGFROM 0.10 TO 0.25% CARBON, FROM 0.10 TO 0.50% SILICON, FROM 0.30 TO 1.0%MANGANESE, FROM 1 TO 14% CHROMIUM, FROM 0.40 TO 1.5% MOLYBDENUM, FROM0.10 TO 0.60% VANADIUM, FROM 0 TO 1% NICKEL, AND MINOR QUANTITIES OFOTHER ELEMENTS SUCH AS SULFUR UP TO 0.030%, PHOSPHORUS UP TO 0.025%,COPPER UP TO 0.20%, THE REMAINDER BEING SUBSTANTIALLY ALL IRON, AT ATEMPERATURE BETWEEN 975* AND 1100* C., COOLING THE STEEL AT A SPEED ATLEAST EQUAL TO 30* C. PER MINUTE BETWEEN 850* AND 600* C., AND THENTEMPERING THE STEEL AT A TEMPERATURE BETWEEN 725* AND 800* C. FOR APERIOD OF TIME SUFFICIENT TO PRODUCE A YIELD POINT BETWEEN 55 AND 65KG./MM.2, ACCORDING TO THE AMOUNT OF CARBON.